Preelectrolysis treatment of pickle liquor



Patented Jan. 22, 1952 PREELECTROLYSIS EATMENT OF PICKLE LIQUOR John '1.Oliver, Berca, Ohio. 'assignor, by mesne assignments, to Union 'Garbideand Carbon fiorporation, a corporation of New York iNo'Drawing.Application March 25, 1947,

Serial No. 737,093

This in ention relates to the elect olysis of waste pick e liquor and tothe treatment of'such liquor to prepare it for electrolysis,particularly electrolysis in a cell of the type shown in my copendingapplication Serial No. 736,939, filed March 25, 19-l'7, wherein thepickle liquor is the electrolyte, and iron is plated from theelectrolyte on a suitable cathode which maybe iron, or iron alloys,copper or any of the commonly-used starting materials for metal plating.

- Iron ispickled by treating it with a water solution of an acid(usually sulphuric acid or, less generally, hydrochloric or other acid)to which has been added an inhibitor, the latter prevent ing ormaterially decreasing the attack of the acid on the clean metal butallowing the acid to attack and remove scale. The Waste pickle liquor,after filtering to remove dirt, scale and other undissolved materials,contains residual pickling acid, the ferrous salt of the acid used and asmall amount of inhibitor. When such a solution is electrolyzed todeposit iron at the cathode, it is difficult to prevent rough depositsand treeing, and to build up desirably thick plates of iron atrelatively high cathode efficiency. I have found that the character ofthe plate may be improved in a very simple manner and with great easeand rapidity and that longer periods of satisfactory cell operationbetween cathode renewals may be obtained by chemically treating thewaste liquor in such a manner as to destroy the corrosion-inhibitingproperties of the inhibiting addition agent in the raw pickle liquor. Itis not at all obvious that treating the pickle liquor to destroy theaction of a benefactive additive (the pickling inhibitor) which assistsin evening the pickling action of the acid on iron (essentially anelectromechanical action) should be beneficial in anotherelectrochemical action,

that is, the plating of iron. Nevertheless, and

more specifically, I have discovered that the desired results can beobtained by treating the pickle liquor before electrolysis with a smallamount of nitrous acid, or of a nitrite which releases nitrous acid inthe pickle liquor under the action of the free pickling acid present inthe waste pickle liquor.

It appears that the nitrite or the nitrous acid very thoroughly removesor kills the inhibitor which is residual in the waste pickle liquor andthat the inhibitor, unless removed, has a bad effect in the electrolysisof the pickle liquor making it difiicult to obtain a deposit in the formof a smooth, thick plate and to prevent treeing. By the removal orkilling ofthe inhibitor is i A test for the sufficiency of the nitriteaddition is to obse ve the evolution of hydrogen on a strip of ironplaced in the liquor; before the addition of the nitrite ve y littlehydrogen forms on the iron, whereas after such addition hydro en isevolved more copiously from the iron. The nitrite may be added in smallincrements to a sample of the liquor until a further addition of thenitrite does not increase the rate at which hydrogen is yielded on theiron. The main body of the liquor is then treated with a. proportionateamount of the nitrite. Smaller amounts of nitrite im rove theelectrolysis over that obtained with no removal of inhibitor; and anexcess of nitrite, at least in moderation, for instance up to 190%,appears to have no undesirable e ect' on the electrolysis. For the usualrun of pickle liouors, 1 gram of sodium nitrite per gallon of pickleliquor has proven adequate, enabling the subsequent electrolysis to beefiected smoothly and efficiently after being properly started. This isabout 0.7 gram of N02 per gallon of lquor whether the N02 be added asnitrous acid or a nitrite.

It is preferred to treat the pickle liouor with nitrites rather thannitrous ac d or its anhydride N203. If the nitrites which are used formprecipitates in the liq or, for instance as the nitrites of barium andstrontium form insoluble sulphates, advantage may be taken of this toremove the metal of the nitrite from the electrolyte Where the nitritesare those of metals such as sodium or potassium which neitherprecipitate nor plate out, the metals will remain in solution; whetheror not such nitrites are to be used, depends upon the purity desi ed inthe final products obtained from the solution. Nitrites of ammonia andsimilar non-metallic bases may also be used, ammonia, in particular,introducin'g no iorei'rn'matter into the final product. Organic"nitrites or nitrito-compounds or the nitroacids'as nitroacetic acid maybe used.

The nitrites may be added to the liquor before or after it is filteredfor pass-age into the cell. It is preferred, however. to add the nitriteto the raw liquor pri'or'to the filtration that precedes electrolysisand thus to remove any insoluble substances that might have been formedby the addition of the nitrite.

Inhibitors which are in frequent use today for commercial pickling areorganic materials; and, while a number of them are proprietary products,typical organic inhibitors are those containing nitrogen, oxygen orsulphur and the other elements of groups 5 and 6 of the periodic tablewhich can form onium compounds (of. Organic Inhibitors of Corrosion byCharles A. Mann, Transactions of The Electrochemical Society, vol. 69,page 115 (1936); also Organic Inhibitors of Corrosion by Mann, Lauer andHultin, Industrial and Engineering Chemistry, vol. 28, pages 159 and1048 (1936)). Organic compounds containing amino or amido (or imino orimido) nitrogen are excellent inhibitors, for instance protein materialsas casein and animal glue or degraded protein materials or syntheticmaterials containing nitrogen of this type, for instance materials ofthe type of those mentioned in the articles previously noted. Excellentinhibitors are those containing both combined sulphur and nitrogen withor Without oxygen or the other elements of groups 5 and 6 of theperiodic table which form onium compounds. These inhibitors aregenerally sulfonated organic compounds containing nitrogen, preferablyin a plurality of basic or amino groups. The organic part of theinhibitor molecule may be of substantially any type but the moleculespresenting long carbon chains are generally the preferred inhibitors.Amino organic acids or their esters or salts, preferably sulfonated, areexcellent inhibitors as they contain combined nitrogen and, wheresulfonated, also contain combined sulphur and oxygen in a relativelylarge molecule. At normal temperatures the inhibitors may be solids orliquids and they are preferably water-soluble or at least partially so.The present invention is principally concerned with inhibitors of any ofthe types mentioned which contain amino groups. Typical inhibitors ofthis type are those referred to in the articles as well as proprietaryinhibitors containing amino groups and selling under such trade names asRodine and Duponol.

Example vWaste sulphate pickle liquor which had been filtered to removedirt, sludge and the like and which contained, per liter, about 80 gramsof ferrous sulphate, 8 grams of free sulphuric acid, and 30 grams ofammonium sulphate and which had been treated with sodium nitrite in theproportion of 1 gram of the nitrite per gallon of liquor produced a goodsmooth non-treeing and non-ridged plate on the cathode of the cell shownin said patent application Serial No. 736,939, and plate thickness inexcess of 4 inch was readily attainable. When the same liquor (exceptthat it had not been treated with the nitrite) was electrolyzed in thesame cell under exactly the same conditions, the plate was rough,characterized by numerous nodules and trees, the latter sufficientlywell developed to give rise to local concentrations of current or evento short-circuits. Also continuous attention and frequent removal ofdeposit were required for cell operation with untreated liquor, as adeposit in excess of inch (usually much less) could not be obtained atcathode efiiciencies of 75% to 85% on continuous operation, which wereobtained with the nitrite-treated liquor.

Though it is possible to electrolyze pickle liquor without killing theinhibitor and, by means of a special cell, for instance a Castner cell,recover the iron (of. Patent No. 2,389,691 to Schumacher and Heise)without the nitrite (or nitrous acid) treatment, iron does not platefrom pickle liquor in the most advantageous manner unless the inhibitoris killed; and, although the inhibitors may be removedfrom pickle liquorin various other ways, the advantages of the present method are its lowcost, effectiveness and simplicity.

The invention is susceptible of modification within the scope of theappended claims.

What is claimed is:

1. In the electrolytic recovery of iron from waste pickle liquorresulting from the commercial acid-pickling of iron in the presence of apickling inhibitor, the step comprising electrodepositing iron on acathode contacting an electrolyte; the electrolyte comprising the wastepickle liquor providing iron ions in aqeous solution for deposition byelectrolysis and also comprising, as an addition agent, a member of thegroup consisting of nitrous acid, its salts and anhydride.

2. In the electrolytic recovery of iron from waste pickle liquorresulting from the commercial acid-pickling of iron in the presence of apickling inhibitor, the step comprising electrodepositing iron on acathode contacting an electrolyte; the electrolyte comprising the wastepickle liquor providing iron ions in aqueous solution for deposition byelectrolysis and also comprising the reaction products of said picklinginhibitor and a member of the group consisting of nitrous acid, itssalts and anhydride, the amount of reaction products corresponding, atleast, to substantially complete reaction of the inhibitor.

3. In the electrolytic recovery of iron from waste pickle liquorresulting from the commercial acid-pickling of iron in the presence of apickling inhibitor, the step comprising electrodepositing iron on acathode contacting an electrolyte; the electrolyte comprising the wastepickle liquor providing iron ions in aqueous solution for deposition byelectrolysis and also comprising the reaction products of said picklininhibitor and a member of the group consisting of nitrous acid, itssalts and anhydride, the amount of reaction products corresponding, atleast, to substantially complete reaction of the inhibitor, theinhibitor being a material containing an element of groups 5 and 6 ofthe periodic table capable of forming an onium compound.

4. In the electrolytic recovery of iron from waste pickle liquorresulting from the commercial acid-pickling of iron in the presence of apickling inhibitor, the step comprising electrodepositing iron on acathode contacting an electrolyte; the electrolyte comprising the wastepickle liquor providing iron ions in aqueous solution for deposition byelectrolysis and also comprising the reaction products of said picklinginhibitor and a member of the group consisting of nitrous acid, itssalts and anhydride, the amount of reaction products corresponding, atleast, to substantially complete reaction of the inhibitor, theinhibitor being an amine.

5. In the electrolytic recovery of iron from waste pickle liquorresulting from the commercial acid-pickling of iron in the presence of apickling inhibitor, the step comprising electrodepositing iron on acathode contacting an electrolyte, the electrolyte comprisin the wastepickle liquor providing iron ions in aqueous solution for deposition byelectrolysis and also comprising, as an addition agent, a member of thegroup con- 5 sisting of nitrous acid, its salts and anhydride, and afree mineral acid.

6. Method of treating waste pickle liquor resulting from the commercialacid-pickling of iron in the presence of a pickling inhibitor toconditicn the liquor for electrolysis which comprises incorporating withthe liquor an addition agent which is a member of the group consistingof nitrous acid, its salts and anhydride, the amount .of addition agentincorporated being sufiicient to materially increase the evolution ofgas when iron is immersed in the pickle liquor containing the additionagent over the amount of gas evolved when iron is immersed in the pickleliquor containing none of said addition agent.

7. Method of treating waste pickle liquor resulting from the commercialacid-pickling of iron to condition the liquor for electrolysis, theliquor containing a nitrogenous corrosion-inhibitor, which comprisesdestroying the corrosioninhibiting properties of said inhibitor byaddingto the liquor a member of the group consisting of nitrous acid,its salts and anhydride.

JOHN P. OLIVER.

6 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 526,114 Placet et al Sept. 18,1894 850,912 Edison Apr. 23, 1907 1,695,430 Klinger Dec. 18, 19281,922,853 Kissel Aug. 15, 1933 2,054,282 Clarkson et al Sept. 15, 19362,147,149 Clapsadle et a1 Feb. 14, 1939 2,306,471 Solomon Dec. 29, 19422,389,691 Schumacher et a1. Nov. 27, 1945 FOREIGN PATENTS Number CountryDate 359,903 Great Britain Apr. 22, 1930 OTHER REFERENCES Holleman,edited by Jamieson and Walker, Textbook of Organic Chemistry, page 89,5th edition, 1920.

1. IN THE RELECTROLYTIC RECOVERY OF IRON FROM WASTE PICKLE LIQUORRESULTING FROM THE COMMERCIAL ACID-PICKLING OF IRON IN THE PRESENCE OF APICKLING INHIBITOR, THE STEP COMPRISING ELECTRODEPOSITING IRON ON ACATHODE CONTACTING AN ELECTROLYTE; THE ELECTORLYTE COMPRISING THE WASTEPICLLE LIQUOR PROVIDING IRON IONS IN AQUEOUS SOLUTION FOR DEPOSITION BYELECTROLYSIS AND ALSO COMPRISING, AS AN ADDITION AGENT, A MEMBER OF THEGROUP CONSISTING OF NITROUS ACID, ITS SALTS AND ANHYDRIDE.